Consolidated Financial Statement Components - Depreciation, Amortization and Accretion (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 2,009	$ 2,066	$ 6,167	$ 6,167
Amortization	625	1,007	2,261	3,153
Accretion	141	156	421	467
Total depreciation, amortization and accretion expense	2,775	3,229	8,849	9,787
Leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciation	50	47	175	145
Asset retirement costs
Property, Plant and Equipment [Line Items]
Depreciation	(97)	(69)	(292)	(209)
Paging and computer equipment
Property, Plant and Equipment [Line Items]
Depreciation	1,990	2,015	6,077	6,010
Furniture, fixtures and vehicles
Property, Plant and Equipment [Line Items]
Depreciation	$ 66	$ 73	$ 207	$ 221